Countercurrent extraction apparatus



Dec. 6, 1955 w. L. THOMAS ET AL COUNTERCURRENT EXTRACTION APPARATUS 4 Sheets-Sheet 1 Filed Aug. 17, 1951 Inventors: William Llewelyn Thomas Peter Desmond Holmes Dec. 6, 1955 w. L. THOMAS ETAL 2,726,145

COUNTERCURRENT EXTRACTION APPARATUS Filed Aug. 17, 1951 4 Sheets-Sheet 2 ZTADMF 1,-Lx. 4 1 X uqum OF 7 DENSITYD2 1 1 F *x L n 13 LmumoF a!" g DENSITY DI D2 I J 16 (I r 323? L H o H l SE arrm Inventors: William Llewelyn Thomas Peter Desmond Holmes Attorneys.

Dec. 6, 1955 2,726,145

W. L. THOMAS ET AL COUNTERCURRENT EXTRACTION APPARATUS Filed Aug. 17, 1951 4 Sheets-Sheet 5 K ii 1 ii:

Inventors: William Llewelyn Thomas Peter Desmond Holmes Attorneys.

Dec. 6, 1955 w. THOMAS ETAL 2,726,145

COUNTERCURRENT EXTRACTION APPARATUS Filed Aug. 17, 1951 4 Sheets-Sheet 4 Fig.12.

Inventors: William Llewelyn Thomas Peter Desmond Holmes Attorneys.

United States Patent COUNTERCURRENT EXTRACTION APPARATUS William Llewelyn Thomas and Peter Desmond Holmes, Sunbury-on-Thames, England, assignors to The British Petroleum Company Limited Application August 17, 1951, Serial No. 242,228

Claims priority, application Great Britain August 23, 195

7 Claims. (Cl. 23-2705) This invention relates to apparatus for the countercurrent extraction of liquid mixtures by means of selective solvents and is of particular application to apparatus for the separation of undesirable constituents from lubricating oil base stocks.

A common form of apparatus for carrying out countercurrent extraction consists of a column which is filled with a packing material in order to promote intimate contact between the solvent and the mixture to be extracted which are introduced at opposite ends of the column. To secure efiicient extraction, it is necessary for the packed height of the column to be considerable and it would obviously be a great advantage if it were possible to reduce the height of the column without reducing the efliciency of extraction or the throughput. With this advantage in mind, a column has been proposed comprising alternate mixing and settling zones, the theory being that the solvent and the mixture are brought into intimate contact in the mixing zones, while the mixture is allowed to separate in the settling zones. In order to secure efficient separation in the settling zones, it has been considered necessary to provide packing in said zones with the result that although it has been possible to reduce the height of the columnwithout loss of extraction efficiency, it has not been possible to operate the column with throughputs as high as those obtainable with the normal packed column. On the other hand, efiicient separation is not achieved merely by the provision of free space zones between the mixing zones.

The present invention seeks to provide a column having alternate mixing and settling zones by means of which the height of the column may be considerably reduced without loss of extraction efliciency or throughput and without the use of packing in the settling zones.

According to the present invention, apparatus for the countercurrent extraction of a liquid mixture by means of a selective solvent consists of a vertical column comprising mixing zones alternating with unobstructed settling zones, means being provided to pass the mixture from each mixing zone to inner intermediate positions in the adjacent settling zones and to direct the mixture outwardly within said settling zones. 7

In using the apparatus according to the invention for the extraction of mixtures of petroleum hydrocarbons, it is preferred to operate with the oil to be extracted as the continuous phase and the solvent as the dispersed phase, the oil being fed in at the base of the column and the solvent at the top. It is possible, however, to operate with the solvent as the continuous phase with the oil passing upwards as the dispersed phase.

In carrying the invention into effect according to one embodiment as applied to the extraction of lubricating oil base stocks, the column is divided into a plurality of zones by means of perforated screens conveniently consisting of wire gauze. The screens are formed with central apertures through which passes a driven shaft centrally located within the column and a paddle is secured to the shaft in alternate zones whereby said zones constiice tute mixing zones. Vertical tubes are secured in the apertures in the perforated screens, said tubes extending into the free spaces between the mixing zones and the tubes in each free space zone terminating a short distance from each other. Secured to the shaft in each free space zone is a double conical baflle member which is located between the ends of the tubes in said zones, said member having a diameter at least equal to the internal diameter of said tubes.

The top and bottom zones in the column are settling zones. The ends of the columnare closed by plates, the top plate carrying the solvent inlet pipe, the rafiinate outlet pipe and a tube for shielding the upper end of the rotor shaft, while the lower plate carries the oil feed inlet pipe and the extract outlet pipe. The solvent may be admitted to the top settling zone or to the top mixing zone and the interface between the two phases may be controlled at a point below the oil feed inlet.

If desired, more than one shaft may be supported within the column, each shaft being provided with bafiie members and with surrounding tubes secured to the perforated screens, as hereinbefore described.

In using the column, the raflinate phase passes up the column as the continuous phase, the solvent passing down the column under gravity. The solvent phase enters each mixing zone via the top gauze of the zone and thorough mixing of the solvent phase with the ascending raffinate phase occurs in this zone. The major part of the solvent phase leaves the mixing zone by passing down the upper tube of the settling zone next below into which it emerges after deflection by the conical bafile. In the settling zone, the bulk of the solvent separates and collects on the bottom gauze of the zone through which it passes to the next mixing zone below. Most of the finely dispersed solvent separates out in the region around the upper tube in the settling zone and collects with the major part of the solvent around the lower tube in said zone. However, some of the solvent phase from each mixing zone passes up the lower tube in the settling zone next above, is deflected outwardly by the conical bafile and collects with the bulk of the solvent phase around said lower tube.

A laboratory column according to the invention will now be described by way of example with reference to the accompanying drawings wherein:

Figure 1 illustrates one arrangement of the column,

Figure 2 illustrates another arrangement of the column,

Figure 3 shows one method of assembling the parts within the column,

Figure 4 shows another method of assembling the parts within the column,

Figure 5 is an enlarged view of the base of the column,

Figure 6 is an enlarged view of the top of the column,

Figures 7 to 10 illustrate various arrangements of multishaft columns,

Figure 11 illustrates diagrammatically the principle on which the columns operate, and

Figure 12 shows a solvent extraction plant incorporat ing a column according to the invention.

Referring first to Figures 1, 5 and 6, the column 10 is divided into mixing zones 11 and settling zones 12 by means of horizontal circular gauze discs 13. Tubes 14 are located in each settling zone and are secured in holes in the discs 13, the upper and lower tubes in each settling zone being equal in length and leaving a short space 15 between their adjacent ends. A rotor shaft 16 passes centrally through the column and double-conical baflles 17 are secured to said shaft and are equally spaced between the pairs of tubes 14. Rotors 18 are secured to the shaft 16 and are centrally located in the mixing zones 11, the rotors being formed with grooves 19 to increase turbulence (Figures 3 and 4).

3 Oil is fed continuously to the base of the column and solvent to thetop, the extract phase, the discontinuous phase, being settled in the zone 20 at the base of the column and the rafiinate phase, the continuous phase,

ur Within. h pa ata H 1 9. 221. .1 92 hal 9! each settling zone is greater than that of the ratfin ate phase surrounding the tube. The rafiinate phase is therefore displaced upwards by gravity and passes through the overflowing from the top of the column, the interphase gauzes separating the mixing and settling zones to the mixbetwcen the two phases being controlled electrically by ing zones where it is brought into contact with an extract means of the electrode 21. The oil is fed through pipe phase which has similarly been displaced from'the settling 22 into the bottom mixing zone 11 and solvent is fed zones above. channelling of the liquid through the through; pipe 23 into the upper tube14 in the top settling central tubes cannot occur because of the rotation ofthe" zone 12. Extract phase leaves the column through, the conical baffles and moreover the' diameters of the latter pipe 24, connected to the bottom end plate 25 and ratfinate are slightly greater than those of the central tubes.

phase leaves the column through the pipe 26 connected The distinguishing characteristic of a column accord to the top end 27. The column is surrounded by a Water ing to the present invention as compared with a Scheibel jacket28 which is provided with an inlet 29 and an outcolumn is that the movement of each phase entering the let 30. mixing zones, and of the mixture of the two phases leav- Referring to Figure 2, the arrangement of the column ing the mixing zones occurs along different paths. is: substantially the same as that of Figure 1 except that Greater limiting throughputs are therefore possible with the upper tubes 14 in the settling zones are longer than this type of column than with those using packedsc'ttling the lower tubes, the position of the bafiles 17 being varied zones. Another advantage is that whereas a s'cheibel col accordingly. This arrangement provides increased seturnn is somewhat troublesome to assemble, afree spate tling capacity for the rafiinate phase at the expense of column according to the present invention canine fabrithe extract phase since it has been found that this differcated in long lengths which are easily mounted of reential between the settling capacities is desirable. moved.

Onemethod of assembling the parts within the column The general arrangement of a solvent extraction plant is illustrated in Figure 3. The gauze discs 13, with the embodying a contacting column according to the present tubes 14' secured thereto, are secured to a length of inv'ention'is diagrammaticallyillustratedin Figure 12'. Oil semi-cylindrical metal foil 31 which fits closely to the is fed from feed tank 33 to the base of the'columuvia wall of the column. This arrangement is apt to give the preheater 34 by means of pump 35 operated bym otor" rise to channelling of solvent between the wall of the n a hermometer 37 being located adjacent the outlet columnandthe foil 31. As shown in Figure 4 therefore, 00 of preheater 34. Solvent is fed from the feed tanks 38 to the gauze discs 14 are secured to a pair of diametrically the top of the column via the preheaterS'Q' by means of opposed. metal rods 32. 7 pump 40' operated by motor 41, a thermometer 42 being" A column comprising a plurality of rotor shafts 16 is located adjacent the outlet of the preheater 39'. The illustrated diagrammatically in Figure 7, the rotors 18 X r bt phase is discharged intostorage at 43 an d' the at eac h level being located in'the same'horizontal plane. rafilnate Phase into Storage f The interface i3 D} 11 Shafts 1 may rotate i h same di qi (Figtrolled by'the electrode 21' which forms part of a level f 10), h am- 1 h f may VIC/[ate i th opposite control circuit 45 comprising a magnetic valve 46' inthe' direction to the surrounding shafts (Figure 9), or each l' p p A theTmOmeteT i5 localiid i113- sliaft of the shafts grouped around the central shaft may Outlet 30 from the f ja k t i TO'IOI Shaft rotate in the opposite direction to the central shaft driven y I 45 Via gears n gear Sh (Figure 8). The arrangement of Figure 8 is preferred 50' Carries a Contact breaker 51 forming P of revilina'stnuch as it produces the smallest extent of vertical PQ C l j -f I p I v movement in the settling zone, such vertical movement A co m Q d F I 'P SeIIt invention an'd' bhl tending to reduce the efficiency in the settling zone. pr g Seven milfingand'eight w l i 101163 9d 5' The principle of operation of a contacting column 40 Process k lh P Y pmp fl h f according to the present invention is diagrammatically u l r F n an isflm-Tmal illustrated in Figure 11-. The oil and solvent passing extractioh temperature of p y' countercurrently to each other become intimately mixed TABFE 1 in each mixing zone. Depending on the ratio of oil 50 I r I I to thgdehnsilty f the resulting mixture assumes Physical propertlesof Oll feealrro'clts' some" value intermediate that of the oil and that of the solvent. Rotation of the conical baffles situated in the Feed 1 Fee-d2 settling zones imparts a centrifugal action to the liquid 7 surrounding them and induces movement of the mixed 55 S iss orii itgflmgj M655- Q9300 Phase fts ss e t hr the e itfitaiiltilfifiiitttttit i1; it? it? tral tubes passing to the mid point; of the settling zones Kinematic Viscosity at210 cs. 37.4, 7.0 (as indicated by the mews in Figure 11). The mix- 99??? j"-jf-f 43 54 ture of the two phases now enters quiescent zones where i l u n separation occurs, the lighter rafiinate phase rising to the Both feedstocks had been dewaxed by known means. top of the settlingzone's, while the heavier extract phase The results of processing feedstock No. 1 are set out m'ov'esdownwards. It will be obvious that the density of in Table 2 below.

TABLE 2 solvnt Raffinate on i Extraction on Tr'eat' Rotor U IJII'LbEYS H'. E. e? t/lif s ggg. li l tli; g g images w a M v Percent 800 7512 72s sis 2f oogjeegotoeco It will be seen that the efiiciency is slightly better at higher solvent treatments, although the oil feed rate appears to have little eflect upon the eificiency. The optimum rotor speed is between 700 and 800 R. P. M.

A comparison between the results obtained by means of a column according to the, present invention and those obtained by means of a similar column but in which the spaces between the mixing zones were entirely filled with A boot eyelet packing, is given in Table 3. i

1 150% solvent treatment.

It will be seen that much lower efficiencies were obtained with the packed column (especially at 300% treatment), since comparable rotor speeds (500-900 R. P. M.), could not be obtained without the column flooding.

In Table 4 below, the efliciency of the present column is compared with that of a Scheibel column of similar diameter having mixing zones alternating with settling zones packed with a roll ofwire gauze.

TABLE 4 [Feedstockz Feed 1.]

Solvent mber of Stages Treatment,

Rotor Extraction speed,

R. P. M.

Temperature, F. Seheibel v Percent 1 Approaching flooding.

TABLE 5- Number of H.E. T. s., Solvent Stages inches Extraction 011 Treat- Temperature, Feedrate, ment,

F. ml./hr. vol. Rotary Packed Rotary Packed Percent 001- 001- 001- Column umn umn umn i 8"? ""53? 20o ""i'' ""ifz's 300 1 7. 5 16 2. 5 9. 0

1 Optimum conditions i. e. rotor speed 700800 R. P. VI.

It will be seen that the height of an equivalent theoretical stage (H. E. T. S.) of the packed column is from 4 to 8 times as great as that of the rotary column.

The effect of varw'ng the mesh of the gauze screens between the zones is set out in Table 6 using feedstock No. 1.

TABLE 6 S 1 t Nlltllbel' of o ven ages T Ertratction F (:il FeIe/d; 'Irgat- RE em eraure, .raem. r.men,vo.

p Percent Gauze Gauze mesh 10 mesh 20 $00 I i 4. 7 5. 3 8% 21% ii? 900 2. 8 140 600 4. 5

1 150% solvent treatment.

It will be seen that a 20 mesh gauze gave inferior results to a 10 mesh gauze. This was probably due to the fact that solvent built up on the lower gauze of the settling zone and did not pass directly through it into the next mixing zone except via the lower tube, hence interfering with the induced circulation caused by the rotating cone.

Two runs were carried out on the column both with and without the deflector cones employing feed No. 2. It is seen from Table 7 below that efficiencies are considerably reduced when the cones are not present.

TABLE 7 Number of Stages TExtraction F ((3111t ggs? 8Rotoir empem e8 m ment vol. pee Without With percent Deflector Deflector Cones Cones- The comparison of column efiiciency employing the two different positions of solvent inlet hereinbefore referred to is given in Table 8.

TABLE 8 Number of Stages Solvent Extraction Oil Treat- Rotor Solvent Inlet in Temperature, Feedrate, ment, peed, Y

F. ml./hr. vol. pter- R. P. M T

' cen D Settlin g ing Zone Zone 1 Column approaching flooding.

agree; 1 45 It is seen that little difference exists between the two except that at lower treatments a higher rotor speed is permissibldwh'en thekolvent inlet is situated in the top settling-zone. I p

The results of extracting two different oil feedstocks in the present column are compared in Table" 9.

1 150%. treatment. 1 Column approaching flooding.

TABLE 10 [Feed employed: Feed L] I.

Flooding oecurred withan oil feed rate (mL/hr.) of

Entree I Solvent, tion Rotor I Tem- Speed, gg F s EBoott Conerature R. P. M. ree pace yec .venp I Percent otary Packed tional Column Rotary Packed Column Column Fr'om the results at 140 F. itis clear that the throughput of the column according to the present invention is greater than the packedrotary column and' at 150 F. the column according to the present inventionhas appioximately the samethroughput as a conventional packed column over the treatment range investigated.

1, Apparatbs for the countercur'rerit extraction of a liquid mixture by means of a selective solvent, consisting of a vertical column, a rotatableshaft located within said column, horizontal perforated partitions within said column' and dividing the column into a plurality of superimposed zones, mixing means secured to said shaft and located in alternate zones only, which are thereby constituted as mixing zones, alignedtubular means concentric with said shaft and secured to said horizontal perforated partitions at one'end with the opposite end extending into the alternatecomplementary zones for passing the mixture from a central position in said mixing zones into a central' position in the complementary alternate zones, said last' mentioned means being in annularly spacedrelation to said shaftand having said opposite ends extending toward one another and terminatinga short distance from each other in said complementary alternate zones, and bafilc means secured togs'aid-rotatable shaft and located between the adjacent ends of said aligned tubular means, means for passing the mixture from said mixing z'ones, said name means directing the mixture outwardly within s'aid 300 above 2,000 2,700

8 a complementary alter'na'te" zones which are thereby'cons'tituteid as settling zones". M

2-. A parahsf for' the counter-current extraction or a liquidmixture'by nicans'of a selective solvent, comprising a vertical" column; horizontal perforated partitions within said column" and dividing-the'column into a plurality of superimposed zories, said horizontal perforated partitions being formed withaligned aperturestherein, a rotatable shaft passing through said column viasaid apertures,mix'- ing means secured to said shaft and located in alternate zones only, which are thereby constituted as mixing zones, aligned tubular members secured to said perforated partitions at one end with the opposite ends extending into the alternate complementaryzone, said tubular members being concentric with and in annularly spaced relation to said shaft for passing the mixture from a central position in said mixing zone into a central position in the complementary alternate zones, said tubular members having saidopposite ends extending toward'one another and terminating a short distance from each other in said comtubular members from the adjacent mixing zones outwardly within the complementary alternate zones which are therebyconstituted as settling zones.

3. Apparatus for the countcrcurrent extraction of a liquid mixture by means of a selective solvent comprising a vertical column, horizontal perforated partitions within said column and dividing the column into a plurality of superimposed zones, said horizontal perforated partitions being formed with aligned apertures therein, a rotatable shaft passing through said column via said apertures, mixing means secured to said shaft and located in alternate tubular members being located in the complementary alternate zones and terminating a short distance from each other, and double-conical baffles secured to said shaft and located in the complementary alternate zones between the adjacent ends of said tubular members, said double-conical baffles being located with their apices directed towards the ends of said tubular members thereby forcing the mixture passing through said tubular members from the adjacent mixing zones outwardly within the complementary alternate zones which are thereby constituted as settling zones.

4. Apparatus for the countercurrent extraction of a liquid mixture by means of a selective solvent comprising a vertical column, horizontal perforated partitions within said column and dividing the column into a p1urality of superimposed zones, said horizontal perforated partitions being formed with aligned apertures therein, a

rotatable shaft passing through said column via said apertures, mixing means secured to said shaft and located in alternate zones, which are thereby constituted as" mixing zones, aligned'tubular members concentric with said shaft and secured in the apertures in said perforated partitions, said'tubula'r members being located in the complementary alternate zones and tefminatinga short distance from each other, and double-conical baffies secured to'said shaft and located in the complementary alternate zones between the adjacent ends of said tubular members, said baffles forcing the mixture passing through said tubular members from the adjacent mixing'zones outwardly within the complementary alternate zones which are therebyc onstituted as' settling zones, the upper tubular members in said settling zones being longer than the lower tubular members in said zones.

said column and 'dividirig'ithe column into plfir l ti' of superimposed zones, said horizontal perforated par'titidn s" being formed with aligned apertures therein, a rotatable shaft passing through said column via said apertures, mixing means secured to said shaft and located in alternate zones, which are thereby constituted as mixing zones, aligned tubular members concentric with said shaft and secured in the apertures in said perforated partitions, said tubular members being located in the complementary alternate zones and terminating a short distance from each other, double conical baffles secured to said shaft and located in the complementary alternate zones between the adjacent ends of said tubular members, said bafiies forcing the mixture passing through said tubular memhers from the adjacent mixing zones outwardly within the complementary alternate zones which are thereby constituted as settling zones, means for supplying a liquid mixture to the base. of the column, and means for supplying a selective solvent to the top of the column.

6. Apparatus for the countercurrent extraction of a liquid mixture by means of a selective solvent comprising a vertical column, horizontal perforated partitions within said column and dividing the column into a plurality of superimposed zones, said horizontal perforated partitions being formed with aligned apertures therein, a rotatable shaft passing-through said column via said apertures, mixing means secured to said shaft and located in alternate zones, which are thereby constituted as mixing zones,-aligned tubular members concentric with said shaft and secured in the apertures in said perforated partitions, said tubular members being located in the complementary alternate zones and terminating a short distance from each other, double conical bafiies secured to said shaft and located in the complementary alternate zones between the adjacent ends of said tubular members, said baffles forcing the mixture passing through said tubular members from the adjacent mixing zones outwardly within the complementary alternate zones which are thereby constituted as settling zones, means for supplying a liquid mixture to the bottom mixing zone, and means for supplying a selective solvent to the top settling zone.

7. Apparatus for countercurrent extraction of a liquid mixture by means of a selective solvent, comprising a vertical column divided into a plurality of alternate mixing and settling zones by means of horizontal perforated partitions having aligned apertures therein, a rotatable shaft passing through said apertures, mixing devices mounted on said shaft and located in said mixing zones only, stationary tubular means located in the settling zones around the apertures in said perforated partitions and in annularly spaced concentric relation to said shaft and secured to said portions at one end with the opposite ends extending into the alternate settling zones, and having said opposite ends extending toward one another and terminating a short distance from each other in said settling zone for passing the mixture from each mixing zone along confined central unobstructed paths into the complementary alternate settling zones, and means also located in the settling zones for causing the mixture thus delivered to the settling zones to be directed outwardly within said zones.

References Cited in the file of this patent UNITED STATES PATENTS 1,993,446 Huff Mar. 5, 1935 2,000,606 Othmer May 17, 1935 2,072,382 Robinson Mar. 2, 1937 2,266,521 Van Dijck Dec. 16, 1941 2,493,265 'Scheibel Jan. 3, 1950 2,569,391 Stearns Sept. 25, 1951 FOREIGN PATENTS 566,945 Germany Dec. 28, 1932 

1. APPARATUS FOR THE COUNTERCURRENT EXTRACTION OF A LIQUID MIXTURE BY MEANS OF A SELECTIVE SOLVENT, CONSISTING OF A VERTICAL COLUMN, A ROTATABLE SHAFT LOCATED WITHIN SAID COLUMN, HORIZONTAL PERFORATED PARTITIONS WITHIN SAID COLUMN AND DIVIDING THE COLUMN INTO A PLURALITY OF SUPERIMPOSED ZONES, MIXING MEANS SECURED TO SAID SHAFT AND LOCATED IN ALTERNATE ZONES ONLY, WHICH ARE THEREBY CONSTITUTED AS MIXING ZONES, ALIGNED TUBULAR MEANS CONCENTRIC WITH SAID SHAFT AND SECURED TO SAID HORIZONTAL PERFORATED PARTITIONS AT ONE END WITH THE. OPPOSITE END EXTENDING INTO THE ALTERNATE COMPLEMENTARY ZONES FOR PASSING THE MIXTURE FROM A CENTRAL POSITION IN SAID MIXING ZONES INTO A CENTRAL POSITION IN THE COMPLEMENTARY ALTERNATE ZONES, SAID LAST MENTIONED MEANS BEING IN ANNULARLY SPACED RELATION TO SAID SHAFT AND HAVING SAID OPPOSITE ENDS EXTENDING TOWARD ONE ANOTHER AND TERMINATING A SHORT DISTANCE FROM EACH OTHER IN SAID COMPLEMENTARY ALTERNATE ZONES, AND BAFFLE MEANS SECURED TO SAID ROTATABLE SHAFT AND LOCATED BETWEEN THE ADJACENT ENDS OF SAID ALIGNED TUBULAR MEANS, MEANS FOR PASSING THE MIXTURE FROM SAID MIXING ZONES, SAID BAFFLE MEANS DIRECTING THE MIXTURE OUTWARDLY WITHIN SAID COMPLEMENTARY ALTERNATE ZONES WHICH ARE THEREBY CONSTITUTED AS SETTLING ZONES. 